The present invention relates generally to a fluid pressure operated actuator mechanism and more particularly to an actuator mechanism for operating a friction clutch.
Friction clutches are commonly used in motor vehicles to transmit rotational power between an engine and a transmission. In one friction clutch design, at least one friction plate is disposed between a clutch pressure plate and an engine flywheel. A clutch housing is attached to the flywheel and includes a clutch spring that is connected to a throw-out bearing for rotation therewith. The clutch spring is typically positioned to apply a clamping force against the pressure plate. Generally, increasing the clamping force against the pressure plate xe2x80x9cengagesxe2x80x9d the clutch, forcing the friction plate into frictional engagement with the flywheel for rotation therewith. Alternatively, decreasing the clamping force against the pressure plate xe2x80x9cdisengagesxe2x80x9d the clutch, permitting the flywheel and friction plate to rotate independent of each other. In order to xe2x80x9cdisengagexe2x80x9d the clutch, an actuator mechanism is typically employed to pivot the clutch spring to a position that decreases the clamping force.
Concentric actuator mechanisms that engage/disengage a friction clutch are known in the art. Conventional concentric actuator mechanisms are generally characterized as either a push-type mechanism or a pull-type mechanism. While both a push-type mechanism and a pull-type mechanism typically employ a clutch spring to generate a clamping force against a pressure plate, they differ markedly in the manner in which the clamping force against the pressure plate is decreased. A push-type concentric actuator mechanism xe2x80x9cpushesxe2x80x9d the bearing toward the clutch causing the clutch spring to pivot away from the pressure plate. In contrast, a pull-type concentric actuator mechanism xe2x80x9cpullsxe2x80x9d the bearing away from the clutch causing the clutch spring to pivot away from the pressure plate. Friction clutches that employ pull-type actuators are advantageous because, unlike clutches that employ push-type actuators, the clamping force exerted by the clutch spring on the pressure plate is biased by the clutch housing, not the bearing. Therefore, a pull-type actuator mechanism is generally considered more efficient because it is possible to obtain a clamping force substantially similar to a push-type actuator with less load on the bearing. While the use of a pull-type actuator advantageously offers a more efficient clutch operation, it also has an undesirable limitation, namely, conventional pull-type concentric actuator mechanisms exhibit a relatively long axial length. Thus, such a limitation inhibits the use of a conventional pull-type actuator with a multiple-plate clutch assembly within a conventional clutch housing.
The present invention provides a pull-type concentric actuator mechanism having a relatively short axial length that permits the use of a multi-plate friction clutch assembly. In accordance with an embodiment of the invention, an actuator mechanism is provided that includes a housing having an annular shaped cylinder therein that possesses a longitudinal axis coaxial with a longitudinal axis of a clutch output shaft. A plurality of intersecting internal fluid ducts cooperate to supply fluid pressure to actuate a piston that is slidably disposed in the cylinder. The piston engages a resilient member that is pivotably secured to a bearing member for movement about a fulcrum member. A clutch spring that engages a pressure plate of the friction clutch is also pivotably secured to the bearing member opposite the resilient member. A source of fluid pressure is provided in communication with the internal fluid ducts for selectively supplying fluid pressure to the cylinder. Upon receipt of fluid pressure, the piston is extended against the biasing force of the resilient member to force the bearing member towards the housing to disengage the clutch. When fluid pressure is removed from the cylinder, the biasing force of the resilient member is operable to cause retraction of the piston into the cylinder. Furthermore, the resilient member forces movement of the bearing away from the housing permitting the clutch spring to engage the pressure plate of the friction clutch.
Among other advantages, the inventive actuator mechanism has a relatively short axial length that permits the use of a multi-plate friction clutch assembly. Moreover, when the clutch is xe2x80x9cengagedxe2x80x9d, the force exerted by the resilient member against the bearing supplements the clamping force exerted by the clutch spring to increase the overall clamping force exerted on the pressure plate. Various additional aspects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.